Concentration
From Eterna Wiki
In the multistrand puzzles, concentration refers to the abundance of the oligo in the mixture. We measure concentration in moles per liter or the number of molecules per a fixed volume. The higher the concentration, the more likely a strand will bind to the target. The lower the concentration, the less likely it will bind.
-Ben: This should probably be edited to be more accurate (I only have a vague notion of concentration)